In a cellular mobile communication system, an evolution from a UMTS (universal mobile telecommunication system) to an LTE (long term evolution) has been devised. In the LTE, an OFDM (orthogonal frequency division multiplexing) and an SC-FDMA (single carrier-frequency division multiple access) are adopted respectively as downlink and uplink radio access technology, thereby enabling a high-speed radio packet communication to be performed at 100 Mb/s or higher for a downlink peak transmission rate and 50 Mb/s or higher for an uplink peak transmission rate. In the 3GPP (3rd Generation Partnership Project) as an international standardization organization, a study of a mobile communication system LTE-A (LTE-Advanced) based on the LTE has been started to realize a further high-speed communication. In the LTE-A, the downlink peak transmission rate of 1 Gb/s and the uplink peak transmission rate of 500 Mb/s are aimed at, and various new techniques are studied on a radio access system, a network architecture, etc. (non-patent documents 1-3). Note that, since the LTE-A is based on the LTE, it is devised to maintain backward compatibility.
Non-Patent Document 1:
    3GPP TR 36.913 V8.0.1 (2009-03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Requirements for further advancements for Evolved Universal Terrestrial Radio Access (E-UTRA) (LTE-Advanced) (Release 8)Non-Patent Document 2:    3GPP TR 36.912 V9.0.0 (2009), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Feasibility study for Further Advancements for E-UTRA (LTE-Advanced) (Release 9)Non-Patent Document 3:    3GPP TR 36.806 V2.0.0 (2010-02), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Relay architectures for E-UTRA (LTE-Advanced) (Release 9)
As one of the methods for establishing a high-speed data communication, the method of deploying a relay station (relay node (RN)) as illustrated in FIG. 1 to support the communication between a base station and a mobile station (non-patent document 2). The relay station relays the communication between a base station (Doner eNB or eNB) and a mobile station (user equipment (UE)), and is provided to support a high-speed data communication. As illustrated in FIG. 2, the link between the mobile station UE and the relay station RN is referred to as a Uu, and the link between the base station (eNB) and the relay station (RN) is referred to as a Un. In the following explanation, the Uu may be referred to as an access link, and the Un may be referred to as a backhaul link.
Various schemes can be implemented to embody a relay station, but for example, a repeater scheme, a decode and forward scheme, an L2 scheme, and an L3 scheme have been studied. The relay station in the repeater scheme has only the function of amplifying a radio signal (data signal and noise). The relay station in the decode and forward scheme has the function of amplifying only a data signal in the radio signal. The relay station in the L2 scheme has the function of the L2 such as a MAC layer etc. The relay station in the L3 scheme has the function of the L3 such as an RRC layer etc., and functions like a base station. The relay station in the L3 scheme is referred to as a Type1 RN in the LTE-A.
A method of evolving a relay station in to a cell is also studied. For example, a method of evolving a relay station to be provided at a cell edge to increase the throughput of the cell edge, a method of evolving a relay station to be provided in a range where radio waves do not reach from the base station locally in a cell (dead spot), etc. are studied.
When data is transmitted between the base station and the mobile station through the relay station (Type1 RN) of the L3 scheme, it is preferable that no self-interference is generated in the relay station in inband relaying in which the same frequency band is shared between the base station and the relay station, and between the relay station and the mobile station. The self-interference (or also called “loop interference”) refers to interference occurring when the relay station receives DL data from the base station to the relay station and simultaneously transmits DL data to the mobile station, and the transmission data appears in a receiver of the relay station, thereby generating interference with the data from the base station. Likewise with the UL data, there can occur the self-interference. When the self-interference occurs, the relay station cannot correctly receive data.
To overcome the problem of the self-interference, the following policies are studied for LTE-A (non-patent document 2).
(A) Downlink: The relay station does not transmit data to the mobile station in the DL backhaul as a subframe for receiving data from an upper base station.
(B) Uplink: The relay station does not receive data from the mobile station in the UL backhaul as a subframe for transmitting data to an upper base station.
Based on the policy (A) above, as illustrated in FIG. 3, when the DL backhaul is configured between the relay station and the base station, the subframe between the relay station and the mobile station is configured as an MBSFN (multicast/broadcast over single frequency network) subframe because, in the MBSFN subframe, the mobile station for the LTE does not receive unicast data. Therefore, since the mobile station UE does not receive a part of a reference signal, it is preferable because it is not necessary to make an unnecessary measurement of the reference signal in the mobile station. That is to say, the relay station can transmit a PDCCH (physical downlink control channel), a PHICH (physical hybrid ARQ indicator channel), a PCFICH (physical control format indicator channel) while it cannot transmit a PDSCH. To receive the control signal, a reference signal is arranged in the first half (CTRL duration illustrated in FIG. 3) of the MBSFN subframe, but it is not arranged in the last half of the MBSFN subframe.
Based on the policy (B) above, control is performed in the relay station not to grant the mobile station permission to transmit UL data before 4 subframes (4 ms) in the UL backhaul because if the mobile station is granted the permission to transmit UL data before 4 ms in the UL backhaul, the mobile station transmits data to the relay station in the UL backhaul, which is to be avoided.
Furthermore, in the relay station, control is performed not to transmit DL data to the mobile station before 4 subframes (4 ms) in the UL backhaul for the following reason. That is, in the HARQ (hybrid automatic repeat request) of the LTE, it is regulated that a receiving station is to return an ACK/NACK signal in 4 ms (4 subframes) after a transmitting station transmits data. Therefore, if DL data is transmitted to the mobile station in 4 ms in the UL backhaul, the mobile station transmits the ACK/NACK signal to the relay station in the UL backhaul, which is to be avoided.
In the UL backhaul, a PUCCH (physical uplink control channel) and a PUSCH (physical uplink shared channel) as control signals to the relay station can be transmitted, but the PUCCH and the PUSCH as control signals from the mobile station cannot be transmitted.
In the actual mobile communication system, there is the situation in which a relay station can cancel the self-interference. This situation is exemplified in FIGS. 4A and 4B.
FIG. 4A illustrates the situation in which, for example, a relay station RN is arranged at the edge of a cell coverage of a base station eNB, and the relay station RN communicates with a mobile station UE outside the cell coverage. In this situation, when the relay station RN transmits data on an access link, the amount of self-interference in the receiver of the relay station RN is limited (limited SI (self-interference)). On the other hand, FIG. 4B illustrates the situation in which, for example, the relay station RN is a mobile relay station RN implemented in a vehicle etc., and a mobile station UE is used in the same vehicle. In this situation, the vehicle itself functions as a shielding plate. Therefore, although the relay station RN transmits data to the mobile station UE in the duration of the DL backhaul (DL_BH subframe), the transmission signal is blocked by the shielding plate, and there is low interference with the signal from the base station. In the situation in which there is a small self-interference amount of the relay station RN, the self-interference can be canceled by the relay station RN. The technique of detecting a desired signal (the received signal from the base station eNB in the example in FIGS. 4A and 4B) by removing the interference component from the received signal, that is, the technique of canceling the self-interference, is well known. Such a technique is described in, for example, the Japanese Laid-open Patent Publication No. 2007-274390.
Configuring a backhaul even in the situation in which the relay station can cancel the self-interference is to limit in excess the communication between the relay station and the mobile station in the backhaul period, which is not preferable because the throughput of the mobile communication system is degraded.